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Archimedes' Law

The force exerted by a fluid on a floating or submerged object is equal to the weight of the water displaced.

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The Weight of Gold

The Weight of Gold

License: CC BY-NC 3.0

Philosopher, mathematician inventor, physicist and engineer, Archimedes contributed to physics with his formulations on hydrostatic and statics. Archimedes is best known for defining what is now known as the buoyant force.

Amazing But True

  • The buoyant force is best described an upward force on an object that is partially or fully submerged. This upward force is due to the pressure difference on the bottom of the object when compared to the top. By measuring the weight of an object in air and in water, you would be able to accurately determine the density of an object as Archimedes did for King Hieron II.
  • King Hieron II tasked Archimedes with determining if the crown made for the king was made of solid gold or if the goldsmith swindled the king and used some silver. Concerned with damaging the crown, Archimedes was initially unable to come up with a solution. His moment of insight came when Archimedes jumped into the bath tub and noticed that the water level rose. He realized that he could use this method to determine the volume of the crown and therefore determine the density. It is reported that Archimedes was so excited that he ran down the street naked, screaming “Eureka”!
  • Watch this amazing story at the link below: 


Can You Apply It?

Using the information provided above, answer the following questions.

  1. Would the effects seen by Archimedes suggest that water is compressible or incompressible?
  2. There are two blocks that are submerged in a body of water. The first block is sitting at the bottom of the body of water while the other block is just under the surface. Which block experiences a greater buoyant force?
  3. If the mass of an object is 10 kg, what volume would it need to have a density of 1 kg / m3?

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  1. [1]^ License: CC BY-NC 3.0

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